The present invention generally relates to a developing apparatus for use in a copying apparatus, printer or the like, based on an electrophotographic copying process, and more particularly, to a developing apparatus arranged to use part of a two or dual-component developing material composed of toner and carrier for developing, while such developing material is transported through circulation.
Conventionally, as a developing apparatus of the above described type, there has been proposed, for example, an arrangement as shown in FIG. 4.
The known developing apparatus 101 in FIG. 4 includes a casing 102, and a developing section 104 formed at a front portion of said casing 102, and having a developing sleeve 105 incorporated therein with a magnet roller (not shown) and disposed to confront a photosensitive surface 100a of a photosensitive or photoreceptor drum 100 as shown. At the rear side of the developing section 104, there are formed a first transport passage 113 and a second transport passage 114 partitioned by a partition wall 107 and communicated with each other through a first path 109 and a second path 111 respectively formed at an inner side and an outer side of the partition wall 107, with first and second screw members 116 and 117 being rotatably provided within the transport passages 113 and 114 respectively.
In the conventional developing apparatus 101 having the construction as described above, the two or dual component developing material composed of toner and carrier is accommodated, and the developing material in the second transport passage 114 is transported in a direction indicated by an arrow X4 based on the rotation of the second screw member 117, and is further transported into the first transport passage 113 along the direction of an arrow X5 through the path 109 at the inner side end portion. Meanwhile, the developing material in the first transport passage 113 is transported in a direction indicated by an arrow Xl based on the rotation of the first screw member 116, and is transported into the second transport passage 114 in a direction of an arrow X3 through the path 111 at the outer side end portion, with part of the developing material being supplied onto the surface of the developing sleeve 105 as the developing material is transported through the transport passage 113. The developing material thus fed onto the developing sleeve 105 is transported in a direction indicated by an arrow X2 based on the rotation of the developing sleeve 105 so as to be led to a developing region P where the developing sleeve 105 confronts the photosensitive surface 100a of the photoreceptor drum 100, and supplies toner to an electrostatic latent image formed on the surface 100a of the drum 100 for the formation of a visible toner image.
On the other hand, in the developing apparatus 101, in order to stably supply the developing material larger than a predetermined amount to the developing section 104 at all times, it is so arranged to make the transport capacity of the developing material by the second screw member 117 larger than that by the first screw member 116, and also to make a cut-out width of the first path 109 larger than that of the second path 111, thereby to maintain the developing material in the first transport passage 113 at a high level.
However, in the prior art developing apparatus 101 as described above, since there is provided no means for adjusting the amount of the developing material to be transported into the first transport passage 113 through the first path 109, the amount of the developing material transported through the first transport passage 113 is directly affected by the reduction of the developing material.
Therefore, when the whole amount of the developing material is reduced as the carrier is gradually decreased as well as the toner through repeated developing functions effected, or when the amount of the developing material is temporarily varied by the toner replenished through the second transport passage 114, its influence directly appears in the amount of the developing material transported to the developing region P, thus resulting in deterioration of image quality due to smearing or fogging, etc. of the copied images.